My sister Thea, is the mystery-loving rodent, not me! But somehow I find myself going undercover to get to the bottom of a case. Slimy Swiss-balls - I hardly knew where to start! Geronimo Stilton, Secret Agent Mouse? Maybe I could get used to that.

In this latest adventure, Geronimo Stilton, the famous newspaper rodent finds that he is being followed by a suspicious-looking rat in a trench coat and dark sunglasses. When he finally confronts his stalker, Geronimo is stunned to realize it is Kornelius von Kickpaw, an old friend from elementary school. Kornelius and his beautiful sister Veronica are secret agents who want to work with Geronimo, but Geronimo has his own problems. He is afraid he has lost the very important envelope sent to him at The Rodent's Gazette, and his grandfather is furious…